Quarries and aggregate suppliers utilize various types of rock crushing equipment to fragment or comminute rocks into various desired sizes or grades of aggregate. Such equipment generally is classified as primary, secondary, or tertiary crushing equipment. Primary crushers include large devices that are sized to receive large rocks and boulders up to about 60 inches in diameter, and are capable of comminuting such rocks or boulders into fragments to less than about 4 inches in diameter. Smaller secondary and tertiary crushers are used to further comminute such reduced fragments to a desired final size or grade.
One common type of rock crusher is a jaw crusher. Jaw crushers typically include a stationary mandrel and an opposed, pivoting jaw that reciprocates between an open position and a crushing position. Rock is fed between the stationary mandrel and pivoting jaw, where the rock is compressed and crushed into smaller fragments. Jaw crushers commonly are used as both primary and secondary crushers.
Gyratory cone crushers typically include a stationary bowl or cone having substantially upright sides and an open top. A central gyrating mandrel within the bowl forms alternating open and closed gaps between the mandrel and the sides of the bowl as the mandrel eccentrically gyrates within the bowl. Rock that is introduced into the open top of the bowl is crushed between the upright sides and the gyrating mandrel as the mandrel reciprocally approaches the upright sides. Like jaw crushers, gyratory cone crushers commonly are used as either primary or secondary crushers.
Roll crushers primarily are used as secondary or tertiary crushers due to their characteristically low reduction ratios. Roll crushers include a plurality of spaced and opposed rolls. Opposed rolls rotate in opposite directions and form a crushing region between the rolls. The rolls may have substantially smooth outer surfaces, or may include cooperating spaced teeth or picks.
Unlike the compressive crushing action of jaw crushers, gyratory cone crushers, and roll crushers, impact crushers crush rock by imparting sudden impact forces to the rock. Horizontal shaft impact crushers typically include one or more rotating horizontal shafts having a plurality of outwardly extending arms or paddles. As the horizontal shafts are rotated at high speeds, rock is fed to the paddles and shattered by the rock's impact with the rapidly moving paddles. Horizontal shaft impact crushers commonly are used as primary, secondary, or tertiary crushers. Because of the high impact forces that are characteristic of such crushers, these devices require substantial periodic maintenance. Vertical shaft impact crushers include a central spindle or drum that is rotated at high speeds. As rock is fed to the center of the rotating spindle, the rock is centrifugally cast at high velocity against a surrounding ring of anvils, where the rock is shattered into fragments. Vertical shaft impact crushers primarily are used as secondary or tertiary crushers.
All of the traditional types of rock crushers described above include electric motors to drive the various types of crushing mechanisms. Due to the large amount of energy required to crush or shatter rock, such electric motors necessarily consume substantial amounts of electric power during operation. Accordingly, the traditional forms of rock crushing equipment described above are not energy efficient. In other words, such devices use brute force to break rock, and require large energy inputs to attain such substantial crushing forces.
Others have attempted to improve the energy efficiency of rock crushing equipment by harnessing the amplified vibratory motion and vibrational energy of various resonant spring-mass systems. For example, U.S. Pat. No. 4,387,859 to Gurries describes a resonantly-powered rock crusher that includes two opposed, elongated pendulous beams having cooperating crushing jaws located at their lower ends. The upper ends of the beams are pinned to a frame such that the beams swing on the frame in a common plane. Oscillatory drivers at the upper, pinned ends of the beams synchronously drive the beams 180 degrees out of phase with each other such that the crushing jaws converge toward and diverge away from each other. The system is driven at a frequency that is slightly below the resonant frequency of the pendulous beams. Unfortunately, such a device has several shortcomings. First, the massive pivotally supported beams described and shown in this patent characteristically must have high natural frequencies and low amplitudes of vibration. Such low amplitudes limit the maximum separation of the crushing jaws, and thereby limit the size of rock that can be introduced between the jaws for crushing. In addition, the oscillatory drivers used to actuate the resonant system necessarily induce forces in the beams that are often misaligned with the beams' swinging motions. Such forces necessarily induce undesirable stresses in the beams, bearings, and frame. Furthermore, only a small fraction of the electric energy supplied to the oscillatory drivers is effectively transferred to the beams for crushing rocks. Accordingly, such a system is less energy efficient than desired.
U.S. Pat. No. 4,026,481 to Bodine describes another rock crushing device that includes two opposed jaws mounted on a pair of opposed horizontal bars. The bars are substantially simply supported at spaced intervals, and are independently driven such that the bars synchronously resonate in a lateral mode. A resonant frequency excitation sets up a standing wave in the bars. The jaws are located on the bars' vibrational antinodes (maximum deflection), and the bars are supported on their vibrational nodes (minimum deflection). This device also appears to include several shortcomings. The device uses independent rotating eccentric weights to excite the bars to resonance. Though the rotating weights induce useful horizontal excitation forces that are in plane with the desired standing waves of the bars, the rotating weights also induce cyclic out-of-plane forces that act to deflect the longitudinal beams in a vertical direction. Because such out-of-plane forces place substantial loads on the device's bars, bearings, and supports, and contribute nothing to the breaking of rock, these forces are both stressful and wasteful. In addition, because the bars must endure substantial deflections in order to provide sufficient spacing between the opposed jaws to receive rock materials for crushing, the bars also are subjected to substantial stresses during operation. Furthermore, the separate independent rotating drivers must be closely synchronized in rotation to cause the bars to vibrate in harmony with one another.
Another rock crushing device that attempts to harness resonant vibrational energy to crush rock is described in U.S. Pat. No. 3,131,878 to Bodine. In one described embodiment, the device includes a stationary anvil or fixed jaw, and a movable jaw. The movable jaw is mounted on the end of an elongated shaft. A vibration generator produces a resonant, longitudinal standing wave in the shaft, thereby causing the movable jaw to cyclically approach and retreat from the fixed jaw. In another described embodiment, the “fixed” jaw is similarly driven at a longitudinal resonant frequency 180 degrees out of phase with the movable jaw. Because the device operates at a high frequency, the resulting jaw displacement must be relatively small. In addition, the device appears to be substantially incapable of imparting substantial impact forces to rock. Accordingly, the device appears incapable of fracturing large rocks, and appears unsuitable for use as a primary crusher.
The conventional crushing devices typically use one or more basic techniques or methods to fracture material such as rocks. Impact crushers, for example, apply high acceleration forces to rock to shatter the rock into smaller fragments. Jaw, cone, gyratory, and roll crushers, on the other hand, use cleavage to squeeze rock at high pressures to fracture the rock. Such cleavage machines also typically cause localized cleavage failure or abrasion that produces fine unwanted particles or fines.
Accordingly, there is a need for an improved crushing device and method that is more reliable and more efficient than known crushing machines. In particular, there is a need for an energy efficient crushing device and method that utilizes resonant vibrational energy to efficiently convert energy inputs into substantial impact and compression forces that are capable of effectively fracturing large rocks. Such a device should be exceptionally durable, and require minimal maintenance. In particular, the device should minimize the use of bearings, gearboxes, sheaves, belts, and other moving parts and mechanical speed reducing equipment. In addition, such a device should operate at an optimum frequency and at an optimum amplitude of vibration to permit the device to effectively fragment both large and smaller rocks by imparting substantial impact and compression forces to the rock. Such a device should apply multiple impacts to crush a rock to provide superior size control and minimize the quantity of fines produced during crushing. In addition, there is a need for an apparatus and method that crushes rock to produce aggregate having a desired size and grade without the need for multiple passes through various forms of crushing equipment. The device and method should apply an optimal combination of shatter and cleavage crushing forces to produce a desired grade of aggregate with a minimum amount of waste or fines.